Canis ISSN: 2398-2942

Dietetic diet: decreasing risk of cystine stones (uroliths)

Contributor(s): Marge Chandler

Pathophysiology

  • These uroliths are composed of the amino acid cystine. The global prevalence of cystine urolithiasis in dogs is approximately 1%, although this varies considerably from country to country.
  • They occur in dogs and cats with cystinuria, which is an inborn error of metabolism characterized by abnormal transport of cystine, a nonessential sulfur-containing amino acid by the renal tubules. Cystine is normally present in low concentrations in plasma. It is freely filtered at the glomerulus and most is actively reabsorbed in proximal tubules. Unlike normal dogs, cystinuric dogs reabsorb a much smaller proportion of cystine from glomerular filtrate and may even have net cystine secretion.
  • Cystine is relatively insoluble in acid urine but becomes more soluble in alkaline urine (above pH 7.2), so urolith formation enhanced by acid urine pH, highly concentrated urine, and incomplete and infrequent micturition. Unless protein intake is severely restricted; cystinuric dogs have no detectable clinical or serum chemistry abnormalities associated with amino acid loss, with the exception of formation of cystine uroliths.
  • The exact mechanism of cystine urolith formation is unknown. Because not all cystinuric dogs form stones, cystinuria is a predisposing factor rather than a primary cause of urolith formation. Urine amino acid profile reveals abnormal quantities of cystine, and in some dogs and cats lysine, arginine and ornithine.
  • Cystine stones are radiolucent to slightly radiopaque and have a smooth to slightly irregular surface Urinalysis cysteine urolith Urinalysis cysteine crystal Urolithiasis: cystine stones.
  • Breeds significantly affected by cystine urolithiasis are the:
  • Males are significantly over-represented with few cases occurring in females.
  • The average age at which cystine urolithiasis occurs is 73 months, with 63% of cases occurring between 37-96 months. In cats, primarily adults are affected (mean age 4 yrs). It is most commonly recognized (although uncommon) in domestic shorthaired cats and Siamese cats.
  • Medical dissolution in dogs involves a combination of N-(2-mercaptopropionly)-glycine (2 MPG) and low protein alkalinizing wet diet to reduce urinary excretion of cystine, promote formation of alkaline urine, and reduce urine concentration.
  • This diet is used in conjunction with 2 MPG for stone dissolution; diet alone is often effective in preventing recurrence. High protein dry diets, especially those rich in methionine, a precursor of cysteine increase the risk of cysteine uroliths. Reduction of dietary protein has the potential of minimizing formation of cystine uroliths. Increased dietary sodium may enhance cystinuria, therefore potassium citrate is better than sodium bicarbonate to maintain alkaline urine (eg pH of 7.5).

Dietary requirements

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Special Considerations

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Recipes

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Further Reading

Publications

Refereed papers
  • Recent references fromPubMed.
  • Hoppe A, Dennenberg T (2001)Cystinuria in the dog: clinical studies during 14 years of medical treatment. JVIM15(4), 361-367PubMed.
  • Osborne C A, Sanderson S L, Lulich J P (1999)Canine cystine urolithiasis: Cause, detection, treatment, and prevention. Vet Clin North Am Small AnimPract29, 193-211PubMed.
  • Bartges J W, Osborne C A, Lulich J P et al(1994)Prevalence of cystine and urate uroliths in bulldogs and urate uroliths in Dalmatians. JAVMA204(12),1914-1918PubMed.
  • Case L C, Ling G V, Franti C E et al(1992)Cystine-containing urinary calculi in dogs: 102 cases (19811989). JAVMA201,129-133PubMed.

Other sources of information

  • Osborne C A, Lulich J P, Albasan H et al(2003)The Role of Nutrition in Management of Lower Urinary Tract Disorders. ACVIM Proceedings 2003.


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